Doctoral candidate Linxiao Zhu, Professor Shanhui Fan and research associate Aaswath Raman are members of the team that invented the breakthrough energy-saving material.

A new ultrathin multilayered material can cool buildings without air conditioning by radiating warmth from inside the buildings into space while also reflecting sunlight to reduce incoming heat.

Stanford University engineers have invented a revolutionary coating material that can help cool buildings, even on sunny days, by radiating heat away from the buildings and sending it directly into space.

A team led by electrical engineering Professor Shanhui Fan and research associate Aaswath Raman reported this energy-saving breakthrough in the journal Nature.

The heart of the invention is an ultrathin, multilayered material that deals with light, both invisible and visible, in a new way.

Invisible light in the form of infrared radiation is one of the ways that all objects and living things throw off heat. When we stand in front of a closed oven without touching it, the heat we feel is infrared light. This invisible, heat-bearing light is what the Stanford invention shunts away from buildings and sends into space.

Of course, sunshine also warms buildings. The new material, in addition dealing with infrared light, is also a stunningly efficient mirror that reflects virtually all of the incoming sunlight that strikes it.

The result is what the Stanford team calls photonic radiative cooling – a one-two punch that offloads infrared heat from within a building while also reflecting the sunlight that would otherwise warm it up. The result is cooler buildings that require less air conditioning.

“This is very novel and an extraordinarily simple idea,” said Eli Yablonovitch, a professor of engineering at the University of California, Berkeley, and a pioneer of photonics who directs the Center for Energy Efficient Electronics Science. “As a result of professor Fan’s work, we can now [use radiative cooling], not only at night but counter-intuitively in the daytime as well.”

The researchers say they designed the material to be cost-effective for large-scale deployment on building rooftops. Though still a young technology, they believe it could one day reduce demand for electricity. As much as 15 percent of the energy used in buildings in the United States is spent powering air conditioning systems.